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  <title>Document</title>
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  <script>
    var str = 'abcde'
    var obj = new String(str)

    function newToString() {
      return 'hello, world'
    }

    function func(val) {
      val.toString = newToString
    }

    func(str)
    console.log(str);

    func(obj)
    console.log(String(obj));
  </script>
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